1. Field of the Invention
This invention relates generally to a still picture transmission device used by connection to a telephone circuit or a PBX (private branch exchange), and particularly to a power supply unit of a visual telephone.
2. Description of the Prior Art
As a conventional device of this kind, there has been available such a device as shown FIG. 1. FIG. 1 is a block diagram showing the basic configuration of a conventional still picture transmission device. In FIG. 1, numeral 1 is a telephone circuit, 2 is an externally equipped telephone, and 3 is an isolating transformer which is provided for isolation from DC, respectively. Numeral 40 is a picture transmission unit, a main control unit, and 6 is a pick-up camera which takes its own pictures (moving pictures). Numeral 7 is a picture control unit which controls selection of either still picture data of a remote station sent from the main control unit 50 or pictures (moving pictures) taken by the pick-up camera. Numeral 8 is a display. Numeral 9 is a transmission switch which performs switching for sending its own pictures (moving pictures) taken by the pick-up camera 6 as a still picture data to the telephone circuit 1. Numeral 10 is an AC adapter and converts a commercial AC 100 V power into DC power. Numeral 11 is a power switch and numeral 12 is a power supply device which supplies necessary power for the device together with the AC adapter 10 and the power switch 11.
The picture transmission unit 40 transmits and receives still picture data through the telephone circuit 1 based on commands from the main control unit 50, and modulates and demodulates still picture data by acting as a modem. The main control unit 50 prepares still picture data for transmission from pictures (moving pictures) developed by pick-up camera.
A still picture transmission device as shown in FIG. 1 needs to be installed at both a calling subscriber side and a called subscriber side.
Next, the operation of the device shown in FIG. 1 will be described. When a call (incoming) from the telephone circuit 1 occurs, the externally equipped telephone 2 informs of this using a ring-back tone. By the call, a called subscriber lifts up a receiver and allows the call from a calling subscriber to be answered.
When a called subscriber receives a message that a calling subscriber to be answered will transmit still pictures, after the called subscriber has confirmed that he has turned the power switch 11 on to apply power to the device, and the unit's own pictures (moving pictures) have been developed and monitored on a display 8, he informs the calling subscriber of completion for the preparation of allowing still picture data to be received. The calling subscriber receives this report and actuates the transmission switch 9 to transmit the still picture data. The still picture data transmitted to the called subscriber side through the telephone circuit 1 are demodulated via the isolating transformer 3 in the picture transmission unit 40 and sent to the main control unit 50. The main control unit 50 informs the picture control unit 7 of the reception of the still picture data. The picture control unit 7 changes-over its own pictures (moving pictures) which have just been transmitted by the camera 6 to the display 8, to the still pictures of this transmitted still picture data from the calling subscriber, and projects them on the display 8. When the still pictures are projected on the display 8, the called subscriber recognizes the reception of the still pictures and returns to the former conversation. When the conversation is completed, he hangs up the externally equipped telephone 2, and the operation ends.
Since the conventional still picture transmission device is configured as described above, even if the called subscriber starts conversation by picking up the receiver in response to a ring-back tone, he does not know whether the telephone on the calling subscriber side is provided with a still picture transmission device or not. Also, even if the caller's telephone is provided with the device, he does not know whether the calling subscriber has the intention of transmitting still pictures or not. Accordingly, he does not know that still pictures have been transmitted until the calling subscriber informs him of the transmission, and then turns power on from the power supply device 12. By this, he has to perform troublesome operation and furthermore, spend unnecessary time until he is able to receive the still pictures.